Method of forming layout design

ABSTRACT

A method of forming a layout design for fabricating an integrated circuit (IC) is disclosed. The method includes identifying one or more areas in the layout design occupied by one or more segments of a plurality of gate structure layout patterns of the layout design; and generating a set of layout patterns overlapping the identified one or more areas. The plurality of gate structure layout patterns has a predetermined pitch smaller than a spatial resolution of a predetermined lithographic technology. A first layout pattern of the set of layout patterns has a width less than twice the predetermined pitch.

BACKGROUND

An integrated circuit (IC) is fabricated according to a layout designusable to form a plurality of masks for selectively forming or removingvarious layers of features, such as active regions, gate electrodes,various layers of isolation structures, and/or various layers ofconductive structures. In some applications, an IC includes transistorshaving different threshold voltages. In one example, the transistors inthe cells along a critical speed path of the IC having lower thresholdvoltages than those in the cells along a non-critical speed path of theIC. In another example, the gate structures at cell boundariesconstitute dummy transistors and are adjusted to have higher thresholdvoltages than other functional transistors for reducing the currentleakage through the dummy transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a diagram of a portion of a layout design of a circuit inaccordance with some embodiments.

FIG. 1B is a diagram of a portion of a layout design of another circuitin accordance with some embodiments.

FIG. 1C is a diagram of a portion of the layout design corresponding tothe circuit of FIG. 1A or FIG. 1B in accordance with some embodiments.

FIG. 2 is a flow chart of a method of forming a layout design inaccordance with some embodiments.

FIGS. 3A-3I are diagrams of portions of various layout designs showingvarious examples for illustrating the operation of the method depictedin FIG. 2 in accordance with some embodiments.

FIGS. 4A-4B are cross-sectional views of portions of different ICsusable for illustrating two different threshold voltage tuning processesin accordance with some embodiments.

FIGS. 5A-5B are cross-sectional views of a portion of an IC usable forillustrating a gate structure trimming process in accordance with someembodiments.

FIG. 6 is a flow chart of a method of fabricating an IC in accordancewith some embodiments.

FIG. 7 is a block diagram of a layout designing system in accordancewith some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In some embodiments, a layout layer usable to for a plurality of gatestructures has a predetermined pitch smaller than a spatial resolutionof a predetermined lithographic technology. Also, a mask layout layerusable for forming a mask defining the areas for performing anelectrical characteristic adjustment process of the resultingtransistors has a minimum pitch equals the predetermined pitch. Comparedwith a mask layout layer having a minimum pitch greater than twice thepredetermined pitch, the cost for forming a mask according the presentdisclosure is greater, but the overall gate density of the resultingintegrated circuit (IC) is higher. In some embodiments, the overall costfor fabricating an IC according to the present disclosure is in factlower than that fabricated according to a mask layout layer having aminimum pitch greater than twice the predetermined pitch.

FIG. 1A is a diagram of a portion of a layout design 100A of a circuitin accordance with some embodiments. Layout design 100A depictsoverlapping layout patterns from various layout layers of layout design100A. Some layout patterns and some layout players of layout design 100Aare simplified or omitted. Layout design 100A depicts a non-limitingexample for facilitating the illustration of the present disclosure.

Layout design 100A includes a first oxide diffusion (OD) layout pattern102, a second OD layout pattern 104, a plurality of gate structurelayout patterns 121, 123, 125, 127, and 129, a plurality of conductivefeature layout patterns 132, 134, 136, 142, 144, and 146, and aplurality of via layout patterns 150. Layout design 100A also includes afirst power layout pattern 162, a second power layout pattern 164, and agate structure cutting layout pattern 166. The components depicted inFIG. 1A are arranged to form two logic cells 172 and 174 encompassed bycell boundaries 176 and 178, respectively.

Cell boundary 176 has an upper edge 176 a (FIG. 1C) running through themiddle of the power layout pattern 162, a lower edge 176 b (FIG. 1C)running through the middle of the power layout pattern 164, a left edge176 c (FIG. 1C) overlapping gate structure layout pattern 121, and aright edge 176 d (FIG. 1C) overlapping gate structure layout pattern125. Cell boundary 178 has an upper edge 178 a (FIG. 1C) running throughthe middle of the power layout pattern 162, a lower edge 178 b (FIG. 1C)running through the middle of the power layout pattern 164, a left edge178 c (FIG. 1C) overlapping gate structure layout pattern 125, and aright edge 178 d (FIG. 1C) overlapping gate structure layout pattern129. In the embodiment depicted in FIG. 1A, the right edge 176 d of cellboundary 176 and the left edge 176 c of cell boundary 178 also overlap.

OD layout pattern 102 is usable to form an N-well region extending alonga direction X through cells 172 and 174; and OD layout pattern 104 isusable to form a P-well region extending along direction X through cells172 and 174. Power layout pattern 162 is usable to form a power railextending along direction X through cells 172 and 174 and configured tocarry a power supply voltage; and power layout pattern 164 is usable toform a power rail extending along direction X through cells 172 and 174and configured to carry a ground reference voltage.

Conductive feature layout pattern 132 is usable to form a conductivefeature connecting the N-well region defined by OD layout pattern 102and the power rail defined by power layout pattern 162 through a viaplug defined by a corresponding via layout pattern 150. Conductivefeature layout pattern 134 is usable to form a conductive featureconnecting the P-well region defined by OD layout pattern 104 and thepower rail defined by power layout pattern 164 through a via plugdefined by a corresponding via layout pattern 150. Conductive featurelayout pattern 136 is usable to form a conductive feature connecting theN-well region defined by OD layout pattern 102 and the P-well regiondefined by OD layout pattern 104. Gate structure layout pattern 123 isbetween conductive feature layout pattern 136 and conductive featurelayout patterns 132 and 134 and is usable to form gate structures overthe N-well region and the P-well region.

Gate structure layout patterns 121, 123, 125, 127, and 129 extend alonga direction Y and have a pitch P_(G) measurable along direction X. Gatestructure layout patterns 121, 123, 125, 127, and 129 are usable to forma plurality of hard mask features or gate electrode features from whicha plurality of gate electrodes is made. In some embodiments, the pitchP_(G) is smaller than a spatial resolution of a predeterminedlithographic technology, and therefore gate structure layout patterns121, 123, 125, 127, and 129 are usable for a multiple-patterning processbased on the predetermined lithographic technology.

Gate structure layout pattern 123, conductive feature layout pattern132, and conductive feature layout pattern 136 are usable of forming aP-type transistor having a source (corresponding to layout pattern 132),a drain (layout pattern 136), and a gate (layout pattern 123). Gatestructure layout pattern 123, conductive feature layout pattern 134, andconductive feature layout pattern 136 are usable of forming an N-typetransistor (corresponding to layout pattern 134), a drain (layoutpattern 136), and a gate (layout pattern 123). The above-listed featurestogether are usable of forming an inverter having an input(corresponding to layout pattern 123) and an output (layout pattern136). As such, cell 172 is an inverter cell.

In cell 174, gate structure layout pattern 127 corresponds to gatestructure layout pattern 123; conductive feature layout pattern 142corresponds to conductive feature layout pattern 132; conductive featurelayout pattern 144 corresponds to conductive feature layout pattern 134;and conductive feature layout pattern 146 corresponds to conductivefeature layout pattern 136. Therefore, gate structure layout pattern127, conductive feature layout pattern 142, and conductive featurelayout pattern 146 are usable of forming a P-type transistor; gatestructure layout pattern 127, conductive feature layout pattern 144, andconductive feature layout pattern 146 are usable of forming an N-typetransistor; and cell 174 is also an inverter cell.

Gate structure layout pattern 125, OD layout pattern 102, and conductivefeature layout patterns 136 and 146 are usable of forming a dummy P-typetransistor 182. Gate structure layout pattern 125, OD layout pattern104, and conductive feature layout patterns 136 and 146 are also usableof forming a dummy N-type transistor 184. In order to isolate cells 172and 174, dummy transistors 182 and 184 are turned off by tying the gateelectrode (corresponding to layout pattern 125) of dummy transistor 182to the power rail (layout pattern 162); tying the gate electrode (layoutpattern 125) of dummy transistor 184 to the power rail (layout pattern164); and removing a portion of the gate electrode corresponding tolayout pattern 125 that is encompassed by gate structure cutting layoutpattern 166.

FIG. 1B is a diagram of a portion of a layout design 100B of a circuitin accordance with some embodiments. Components in FIG. 1B that are thesame or similar to those in FIG. 1A are given the same or similarreference numbers. Layout design 100B depicts another non-limitingexample for facilitating the illustration of the present disclosure.

Compared with layout design 100A, in layout design 100B, the OD layoutpattern 102 and 104 are replaced and/or supplemented by fin structurelayout patterns 106 and 108. Fin structure layout patterns 106 and 108are usable to form a plurality of fin structures over a substrate of thecircuit. The resulting transistors fabricated according to layout design100B have a multi-gate architecture and sometimes also known as FinFETs.

FIG. 1C is a diagram of a portion of the layout design 100Ccorresponding to the circuit of FIG. 1A or FIG. 1B in accordance withsome embodiments. Components in FIG. 1C that are the same or similar tothose in FIG. 1A of FIG. 1B are given the same or similar referencenumbers. Layout design 100C summarizes the examples as illustrated inFIGS. 1A and 1B and de-emphasized or omitted various layout patterns inFIGS. 1A and 1B for facilitating the illustration of the presentdisclosure.

As illustrated above in conjunction with FIG. 1A, the dummy transistors182 and 184 corresponding to gate electrode structure layout pattern 125are turned off. To reduce the leakage current through the dummytransistors 182 and 184, the dummy transistors are subject to be furtherprocessed to increase their threshold voltages. Therefore, layoutpatterns 192 and 194 are introduced to define the areas subject to anelectrical characteristic tuning process. In some embodiments, thelayout patterns 192 and 194 are also usable for adjusting the electricalcharacteristics of functional transistors, such as the transistorsconstituting the P-type and N-type transistors of the inverterscorresponding to gate structure layout pattern 123 and 127.

In some embodiments, layout patterns 192 and 194 are usable to defineopenings in a mask layer that expose the areas subject to the electricalcharacteristic tuning process. In some embodiments, layout patterns 192and 194 are usable to define blocking areas in a mask layer for exposingthe areas on which the electrical characteristic tuning process will beperformed. In some embodiments, the electrical characteristic tuningprocess is usable for leakage reduction of a dummy transistor of the ICor power adjustment of a functional transistor of an integrated circuit.In some embodiments, suitable electrical characteristic tuning processesincludes a threshold voltage tuning process or a gate structure trimmingprocess. In some embodiments, the affected electrical characteristics ofthe transistors underwent the tuning processes includes theircorresponding threshold voltages, turned-on current, or leakage current.

In some embodiments, layout patterns 192 and 194 have a width W₁ lessthan twice the pitch P_(G). In some embodiments, width W₁ equals pitchP_(G). In some embodiments, layout patterns 192 and 194 are formed on amask layout layer, and the mask layout layer has a minimum pitch equalspitch P_(G).

FIG. 2 is a flow chart of a method 200 of forming a layout design inaccordance with some embodiments. It is understood that additionaloperations may be performed before, during, and/or after the method 200depicted in FIG. 2, and that some other processes may only be brieflydescribed herein.

Method 200 begins with operation 210, where one or more areas in thelayout design occupied by one or more segments of a plurality of gatestructure layout patterns of the layout design are identified. The oneor more identified areas correspond to one or more regions of the ICsubject to an electrical characteristic tuning process for fabricatingthe IC. In some embodiments, the purpose of performing the electricalcharacteristic tuning process is to increase or decrease thresholdvoltages of corresponding transistors.

The method proceeds to operation 220, where a set of layout patternsoverlapping the one or more areas is generated in a mask layout layer ofthe layout design. The plurality of gate structure layout patterns has apredetermined pitch. The set of layout patterns has a minimum pitchequals to the predetermined pitch. In some embodiments, a width of afirst layout pattern of the set of layout patterns or a gap between thefirst layout pattern and a second layout pattern set of layout patternsis less than twice the predetermined pitch of the plurality of gatestructure layout patterns. In some embodiments, the width of the firstlayout pattern of the set of layout patterns is an integer multiple ofthe predetermined pitch. In some embodiments, the gap between the firstlayout pattern and the second layout pattern set of layout patterns isan integer multiple of the predetermined pitch.

Implementation of the method 200 of FIG. 2 will now be explained by wayof several examples. FIGS. 3A-3I are diagrams of portions of variouslayout designs in accordance with some embodiments.

FIG. 3A is a diagram of a portion of a layout design 300A forfabricating an IC in accordance with some embodiments. Layout design300A is usable to show various example layout patterns in the masklayout layer generated according to method 200.

Layout design 300A includes a power layout pattern 302 corresponding topower layout pattern 164 in FIGS. 1A-1C, a first OD layout pattern 304Ucorresponding to OD layout pattern 104, and a second OD layout pattern304L also corresponding to OD layout pattern 104 and being an mirroredlayout pattern of OD layout pattern 304U about power layout pattern 302.A reference line 306 corresponding to edges of logic cells, such as edge176 b and 178 b, runs through the middle of the power layout pattern302.

Layout design 300A further includes a plurality of gate structure layoutpatterns 310 a-310 s and a set of layout patterns 320 a-320 m generatedby a process corresponding to method 200. The plurality of gatestructure layout patterns 310 a-310 s extends along a direction Y andhas a predetermined pitch P_(G) measurable along a direction X. In someembodiments, the pitch P_(G) is smaller than a spatial resolution of apredetermined lithographic technology, and therefore gate structurelayout patterns 310 a-310 s are usable for a multiple-patterning processbased on the predetermined lithographic technology.

One or more areas in the layout design 300A occupied by one or moresegments 312 a-312 m of the plurality of gate structure layout patterns310 a-310 s are identified such that the one or more segments 312 a-312m indicate the corresponding transistors that are subject to electricalcharacteristic tuning. An electrical characteristic tuning process willbe performed for fabricating the IC, and the set of layout patterns 320a-320 m corresponds to one or more openings or blocking features to beformed in a mask layer prior to performing the electrical characteristictuning process.

Each layout pattern of the set of layout patterns 320 a-320 m has awidth W₁ measurable along the direction X. Width W₁ is less than twicethe predetermined pitch P_(G). In some embodiments, width W₁ equalspredetermined pitch P_(G). The set of layout patterns 320 a-320 mdemonstrates some of many possible layout combinations of the layoutpatterns of the mask layout layer.

In one example, layout pattern 320 a has an edge overlapping a cellboundary represented by reference line 306 without abutting any otherlayout patterns of the mask layout layer. In another example, layoutpatterns 320 b and 320 c each have an edge overlapping the cell boundary306, and layout patterns 320 b and 320 c abut each other at thecorresponding edges that overlap cell boundary 306.

In another example, layout patterns 320 d and 320 e each have an edgeoverlapping the cell boundary 306, and a corner of layout pattern 320 eand a corner of layout pattern 320 e on the edges overlapping cellboundary 306 abut each other. In another example, layout patterns 320 fand 320 g have an arrangement similar to that of layout patterns 320 dand 320 e except being mirrored about a reference axis in parallel withthe direction Y.

In another example, layout patterns 320 h, 320 i, and 320 j each have anedge overlapping the cell boundary 306. A left corner of layout pattern320 i and a corner of layout pattern 320 h on the edges overlapping cellboundary 306 abut each other; and a right corner of layout pattern 320 iand a corner of layout pattern 320 j on the edges overlapping cellboundary 306 abut each other. Layout patterns 320 h and 320 j areseparated by a gap having a width W₂ measurable along the direction X.Width W₂ is less than twice the predetermined pitch P_(G). In someembodiments, width W₂ equals predetermined pitch P_(G). In anotherexample, layout patterns 320 k, 320 l, and 320 m have an arrangementsimilar to that of layout patterns 320 h, 320 i, and 320 j except beingmirrored about a reference axis in parallel with the direction X.

FIGS. 3B-3I are diagrams of portions of layout designs 300B-300I inaccordance with some embodiments. FIGS. 3B-3I depicts more examplelayout patterns as combinations based on the examples depicted in FIG.3A. Components in FIGS. 3B-3I that are the same or similar to those inFIG. 3A are given the same or similar reference numbers. Referencenumbers for gate structure layout patterns and OD layout patterns areomitted for clarity.

In FIG. 3B, layout design 300B includes a set of layout patterns 330a-330 g for forming the mask layer as illustrated above. Each layoutpatterns of the set of layout patterns 330 a-330 g has a width W₁ and isarranged along the reference line 306. Layout patterns 330 a-330 g abutone another only at the corresponding corners overlapping cell boundaryrepresented by reference line 306. Layout patterns 330 a, 330 c, 330 e,and 330 g are separated from one another by corresponding gaps having awidth W₂. Layout patterns 330 b, 330 d, and 330 f are separated from oneanother by corresponding gaps having a width W₂. In some embodiments,width W₁ and width W₂ equal the predetermined pitch P_(G) of the gatestructure layout patterns.

In FIG. 3C, compared with layout design 300B, layout patterns 330 c and330 e are replaced by layout pattern 330 h in layout design 300C. Layoutpattern 330 h corresponds to an area covering three consecutive gatestructure layout patterns and suitable to accommodate three unit layoutpatterns that has a width of the predetermined pitch P_(G). Here, layoutpattern 330 h has a width W₃ equals three times of the predeterminedpitch P_(G).

In FIG. 3D, compared with layout design 300C, layout patterns 330 b-330f are replaced by layout pattern 330 i in layout design 300D. Layoutpattern 330 i corresponds to an area covering five consecutive gatestructure layout patterns and suitable to accommodate five unit layoutpatterns (such as layout pattern 320 a in FIG. 3A) that has a width ofthe predetermined pitch P_(G). Here, layout pattern 330 i has a width W₄equals five times of the predetermined pitch P_(G).

In FIG. 3E, compared with layout design 300C, layout patterns 330 d and330 f are replaced by layout pattern 330 j in layout design 300E. Layoutpattern 330 j corresponds to an area covering two consecutive gatestructure layout patterns and suitable to accommodate two unit layoutpatterns that has a width of the predetermined pitch P_(G). Moreover,layout pattern 330 b and 330 j are separated by a gap having a width W₅.The gap between layout pattern 330 b and 330 j extends over an areacorresponding to two consecutive gate structure layout patterns andsuitable to accommodate two unit layout patterns that has a width of thepredetermined pitch P_(G). Here, the width W₅ of the gap equals twotimes of the predetermined pitch P_(G).

As a variation of the embodiments depicted in FIG. 3C and FIG. 3D, insome embodiments, a layout pattern has a width that is an integermultiple of the predetermined pitch P_(G). As a variation of theembodiment depicted in FIG. 3E, in some embodiments, two layout patternsare separated by a gap having a width that is an integer multiple of thepredetermined pitch P_(G).

For example, in FIG. 3F, compared with layout design 300E, layoutpattern 330 h is replaced by layout pattern 330 k in layout design 300F.Layout pattern 330 k has a width of twice the predetermined pitch P_(G)instead of three times of the predetermined pitch P_(G) as layoutpattern 330 h. A gap between layout pattern 330 k and layout pattern 330g has a width of twice the predetermined pitch P_(G). In yet anotherexample as depicted in FIG. 3G, compared with layout design 300E, layoutpatterns 330 b and 330 j are replaced by layout pattern 3301 in layoutdesign 300G. Layout pattern 3301 has a width of seven times thepredetermined pitch P_(G).

FIG. 3H depicts yet another example layout design 300H, which includeslayout patterns 330 a, 330 m, 330 n, and 330 o. Layout pattern 330 a hasa width of a single predetermined pitch P_(G). Layout pattern 330 m hasa width of four times the predetermined pitch P_(G). Layout pattern 330n has a width of three times the predetermined pitch P_(G). Layoutpattern 330 m has a width of twice the predetermined pitch P_(G). Layoutpattern 330 n abuts layout pattern 330 a and layout pattern 330 m atcell boundary 306. Layout pattern 330 m abuts layout pattern 330 n aswell as layout pattern 330 o at cell boundary 306. Layout pattern 330 aand layout pattern 330 m are separated by a gap having a width of asingle predetermined pitch P_(G). Layout pattern 330 n and layoutpattern 330 o are separated by a gap having a width of twice thepredetermined pitch P_(G).

FIG. 3I depicts yet another example layout design 300I, which includeslayout patterns 330 l, 330 p, 330 r, and 330 g. Layout pattern 330 g hasa width of a single predetermined pitch P_(G). Layout pattern 330 l hasa width of seven times the predetermined pitch P_(G). Layout pattern 330p has a width of twice the predetermined pitch P_(G). Layout pattern 330r has a width of twice the predetermined pitch P_(G). Layout pattern 330l abuts layout patterns 330 p, 330 r, and 330 g at cell boundary 306.Layout pattern 330 p and layout pattern 330 r are separated by a gaphaving a width of a single predetermined pitch P_(G). Layout pattern 330r and layout pattern 330 g are separated by a gap having a width of asingle predetermined pitch P_(G).

FIG. 4A is a cross-sectional view of a portion of an IC 400A usable forillustrating a first example threshold voltage tuning processes inaccordance with some embodiments. FIG. 4A is taken along a referencesurface that does not cut through the corresponding gate structures.

IC 400A includes a substrate 410, a plurality of fin structures 412,414, and 416 protruding from an upper surface 410 a of substrate 410, anisolation layer 422 over the upper surface 410 a of substrate 410 andpartially cover the fin structures 412, 414, and 416, and a mask layer424 over isolation layer 422 and fin structures 412 and 416. Variouscomponents in IC 400A are arranged in a first transistor region 432, asecond transistor region 434, and a third transistor region 436. Firsttransistor region 432 corresponds to a transistor of a first type, andsecond transistor region 434 and third transistor region 436 correspondto transistor of a second type. In some embodiments, a transistor of thefirst type refers to an N-type transistor, and a transistor of thesecond type refers to a P-type transistor. In some embodiments, atransistor of the first type refers to a P-type transistor, and atransistor of the second type refers to an N-type transistor.

Mask layer 424 has an opening 426 defined therein and exposing a portionof fin structures 414. In some embodiments, the mask layer 422 is formedaccording to a mask layout layer including the set of layout patterns320 a-320 m in FIG. 3A, or 330 a-330 h in FIGS. 3B-3G. In someembodiments, the opening 426 is defined according to the set of layoutpatterns 320 a-320 m or 330 a-330 h. In FIG. 4A, transistors to beformed in transistor regions 434 and 436 are of the same type. However,the transistor formed in transistor region 434 is exposed by the opening426 and thus will be process to adjust the electrical characteristicthereof.

For example, an implantation process 440 is performed to adjust aneffective doping concentration at fin structures 414. In someembodiments, implantation process 440 increases or decrease theeffective doping concentration at fin structures 414 in compression witha counterpart fin structures 416 usable to form transistors of the sametype. As a result, a threshold voltage of the resulting transistor attransistor region 434 is different from that of the transistor intransistor region 436. In some embodiments, if the resulting transistorsin regions 434 and 436 are N-type transistors, increasing P-type dopingconcentration of fin structure 414 results in a smaller thresholdvoltage, and decreasing P-type doping concentration of fin structure 414results in a greater threshold voltage. In some embodiments, if theresulting transistors in regions 434 and 436 are P-type transistors,increasing N-type doping concentration of fin structure 414 results in asmaller threshold voltage, and decreasing N-type doping concentration offin structure 414 results in a greater threshold voltage.

FIG. 4B is a cross-sectional view of a portion of an IC 400B usable forillustrating a second example threshold voltage tuning processes inaccordance with some embodiments. Components in FIG. 4B that are thesame or similar to those in FIG. 4A are given the same referencenumbers. FIG. 4B is taken along a reference surface that cuts throughthe corresponding gate structures 452, 454, and 456.

Compared with IC 400A, instead of performing implantation process 440 inthe opening 426, gate electrode structure 454 is formed to havedifferent material and/or structure than those of electrode structure452 and 456. In some embodiments, gate electrode structure 454 has amaterial having a work function metal different than that of gateelectrode 456. As a result, a threshold voltage of the resultingtransistor at transistor region 434 is different from that of thetransistor in transistor region 436.

In some embodiments, the processes as illustrated in FIGS. 4A and 4B areboth performed to adjust the threshold voltage of a transistor in an IC.In some embodiments, only one of the processes as illustrated by FIGS.4A and 4B is performed to adjust the threshold voltage of a transistorin an IC.

In some embodiments, the dummy transistors corresponding to dummytransistors 182 and 184 in FIG. 1A-1C will be exposed or blockedaccording to the layout patterns corresponding to layout patterns 192and 194 when performing the threshold voltage tuning processes.

FIGS. 5A-5B are cross-sectional views of a portion of an IC 500 usablefor illustrating a gate structure trimming process in accordance withsome embodiments.

In FIG. 5A, IC 500 includes a substrate 510, a polysilicon layer 520over substrate 510, a plurality of hard mask features 532 a-532 f overpolysilicon layer 520, and a mask layer 542 over polysilicon layer 520and hard mask features 532 a-532 c and 532 e-532 f. Hard mask features532 a-532 f are patterned according to a plurality of gate structurelayout patterns, such as layout patterns 121-129 (FIG. 1) or 310 a-310 s(FIG. 3A). Mask layer 542 has an opening 544 defined therein, andopening 544 is formed according to a mask layout layer having a set oflayout patterns, such as layout patterns 320 a-320 m (FIG. 3A) or 330a-330 h (FIGS. 3B-3G). In FIG. 5A, a first etching process 550 isperformed to reduce a width of hard mask features 532 d.

In FIG. 5B, after the first etching process, hard mask features 532 d istrimmed to become hard mask features 532 d′, which has a smaller width.Mask layer 542 is removed, and then a second etching process 550 isperformed to pattern polysilicon layer 520 into a plurality ofpolysilicon features 522-522 f. Polysilicon features 522 a-522 f areusable as gate structures or dummy gate structures subject to asubsequent gate replacement process. Because polysilicon feature 522 dhas a width smaller than that of other polysilicon features 522 a-522 cand 522 e-522 f, a resulting transistor corresponding to polysiliconfeature 522 d has a faster operating speed than resulting transistors ofthe same type corresponding to polysilicon feature 522 a-522 c and 522e-522 f.

In some embodiments, the dummy transistors corresponding to dummytransistors 182 and 184 in FIG. 1A-1C will be blocked according to thelayout patterns corresponding to layout patterns 192 and 194 whenperforming the gate structure trimming process.

FIG. 6 is a flow chart of a method 600 of fabricating an IC inaccordance with some embodiments. It is understood that additionaloperations may be performed before, during, and/or after the method 600depicted in FIG. 6, and that some other processes may only be brieflydescribed herein.

Method 600 begins with operation 610, where a plurality of patternedfeatures is formed according to a plurality of gate structure layoutpatterns, such as layout patterns 121-129 (FIG. 1) or 310 a-310 s (FIG.3A). The plurality of patterned features is formed using amultiple-patterning process based on a predetermined lithographictechnology. The plurality of patterned features thus extends along afirst direction corresponding to direction Y in FIG. 3A and has apredetermined pitch corresponding to pitch P_(G) in FIG. 3A measurablealong direction X. In some embodiments, the pitch P_(G) is smaller thana spatial resolution of the predetermined lithographic technology. Insome embodiments, the plurality of patterned features corresponds tohard mask features 532 a-532 f in FIG. 5A or polysilicon features formedaccording to hard mask features 522 a-522 f.

The process proceeds to operation 620, where a mask layer is formed overthe plurality of patterned features. The mask layer includes one or moreopenings defined therein, and the one or more openings exposing one ormore areas corresponding to one or more segments of the plurality ofpatterned features. In some embodiments, the mask layer corresponds tomask layer 542 in FIG. 5A with opening 544 defined therein. The one ormore openings are defined according to a set of layout patterns of amask layout layer, such as layout patterns 320 a-320 m or 330 a-330 l inFIGS. 3A-3G. Therefore, in some embodiments, the one or more openingshave a minimal pitch that equals the predetermined pitch P_(G) of theplurality of patterned features.

The process proceeds to operation 630, where an electricalcharacteristic tuning process is performed on the exposed one or moreareas. In some embodiments, the electrical characteristic tuning processcomprises a threshold voltage tuning process as illustrated inconjunction with FIGS. 4A and 4B or a gate structure trimming process asillustrated in conjunction with FIG. 5.

FIG. 7 is a block diagram of a layout designing system 700 in accordancewith some embodiments. Layout designing system 700 is usable forimplementing the method disclosed in FIG. 2 and further explained inconjunction with FIG. 1 and FIGS. 3A-3G.

System 700 includes a hardware processor 710, a non-transitory, computerreadable storage medium 720, an input/output interface 730 coupled toexternal circuitry, and a network interface 740 communicatively coupledwith one another through a bus 750.

Storage medium 720 is encoded with a set of executable instructions 722.The processor 710 is configured to execute the set of executableinstructions 722 in order to cause system 700 to be usable forperforming a portion or all of the operations as depicted in FIG. 2. Insome embodiments, the processor 710 is a central processing unit (CPU),a multi-processor, a distributed processing system, an applicationspecific integrated circuit (ASIC), and/or a suitable processing unit.

In some embodiments, the computer readable storage medium 720 is anelectronic, magnetic, optical, electromagnetic, infrared, and/or asemiconductor system (or apparatus or device). For example, the computerreadable storage medium 720 includes a semiconductor or solid-statememory, a magnetic tape, a removable computer diskette, a random accessmemory (RAM), a read-only memory (ROM), a rigid magnetic disk, and/or anoptical disk. In some embodiments using optical disks, the computerreadable storage medium 720 includes a compact disk-read only memory(CD-ROM), a compact disk-read/write (CD-R/W), and/or a digital videodisc (DVD).

In some embodiments, the storage medium 720 stores the set of executableinstructions 722 configured to cause system 700 to perform a method asdepicted in FIG. 2. In some embodiments, the storage medium 720 alsostores information needed for performing method 200 or generated duringperforming the method, such as layout design files 724, identifiedsegments of gate structure layout patterns 726, and/or any intermediatedate 728.

Network interface 740 allows system 700 to communicate with a network760, to which one or more other computer systems are connected. Networkinterface 740 includes wireless network interfaces such as BLUETOOTH,WIFI, WIMAX, GPRS, or WCDMA; or wired network interface such asETHERNET, USB, or IEEE-1394. In some embodiments, the method of FIG. 2is implemented in two or more system, and executable instructions orlayout design information are exchanged between different systems 700via the network 760.

In accordance with one embodiment, a method of forming a layout designfor fabricating an integrated circuit (IC) is disclosed. The methodincludes identifying one or more areas in the layout design occupied byone or more segments of a plurality of gate structure layout patterns ofthe layout design; and generating a set of layout patterns overlappingthe identified one or more areas. The one or more areas correspond toone or more regions of the IC subject to an electrical characteristictuning process for fabricating the IC. The plurality of gate structurelayout patterns extends along a first direction and has a predeterminedpitch measurable along a second direction. The predetermined pitch issmaller than a spatial resolution of a predetermined lithographictechnology. The set of layout patterns corresponds to one or moreopenings to be formed in a mask layer prior to performing the electricalcharacteristic tuning process. A first layout pattern of the set oflayout patterns has a width measurable along the second direction, andthe width of the first layout pattern is less than twice thepredetermined pitch.

In accordance with another embodiment, a method of forming a layoutdesign for fabricating an integrated circuit (IC) is disclosed. Themethod includes identifying one or more areas in the layout designoccupied by one or more segments of a plurality of gate structure layoutpatterns of the layout design; and generating a set of layout patternsoverlapping the identified one or more areas. The one or more areascorrespond to one or more regions of the IC subject to an electricalcharacteristic tuning process for fabricating the IC. The plurality ofgate structure layout patterns extends along a first direction and has apredetermined pitch measurable along a second direction. Thepredetermined pitch is smaller than a spatial resolution of apredetermined lithographic technology. The set of layout patternscorresponds to one or more openings to be formed in a mask layer priorto performing the electrical characteristic tuning process. A firstlayout pattern and a second layout pattern of the set of layout patternsare separated by a first gap along the second direction, and a width ofthe first gap measurable along the second direction is less than twicethe predetermined pitch.

In accordance with another embodiment, a layout design for fabricatingan integrated circuit (IC) is disclosed. The Layout design includes afirst layout layer and a second layout layer. The first layout layerincludes a plurality of gate structure layout patterns. The plurality ofgate structure layout patterns extends along a first direction and has apredetermined pitch measurable along a second direction, and thepredetermined pitch is smaller than a spatial resolution of apredetermined lithographic technology. The second layout layer includesa set of mask layout patterns arranged based on one or more openingregions. The one or more opening regions overlap one or more of theplurality of gate structure layout patterns corresponding to one or moregate structures subject to an electrical characteristic tuning process.A first mask layout pattern of the set of mask layout patterns has awidth measurable along the second direction, and the width of the firstmask layout pattern is equal to the predetermined pitch.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of forming a layout design forfabricating an integrated circuit (IC), the method comprising:identifying one or more areas in the layout design occupied by one ormore segments of a plurality of gate structure layout patterns of thelayout design, the one or more areas corresponding to one or moreregions of the IC subject to an electrical characteristic tuning processfor fabricating the IC, the plurality of gate structure layout patternsextending along a first direction and having a predetermined pitchmeasurable along a second direction, and the predetermined pitch beingsmaller than a spatial resolution of a predetermined lithographictechnology; and generating a set of layout patterns overlapping theidentified one or more areas, the set of layout patterns correspondingto one or more openings to be formed in a mask layer prior to performingthe electrical characteristic tuning process, a first layout pattern ofthe set of layout patterns having a width measurable along the seconddirection, and the width of the first layout pattern being less thantwice the predetermined pitch.
 2. The method of claim 1, wherein asecond layout pattern of the set of layout patterns has a widthmeasurable along the second direction, and the width of the secondlayout pattern being an integer multiple of the predetermined pitch. 3.The method of claim 1, wherein the electrical characteristic tuningprocess is usable for leakage reduction of a dummy transistor of the ICor power adjustment of a functional transistor of the IC.
 4. The methodof claim 1, wherein the set of layout patterns comprises a second layoutpattern; the first layout pattern has an edge overlapping a cellboundary of the layout design; and the second layout pattern has an edgeoverlapping the cell boundary of the layout design.
 5. The method ofclaim 4, wherein the edge of the first layout pattern and the edge ofthe second layout pattern abutting each other.
 6. The method of claim 4,wherein a first corner of the first layout pattern on the edge of thefirst layout pattern and a corner of the second layout pattern on theedge of the second layout pattern abutting each other.
 7. The method ofclaim 6, wherein the set of layout patterns further comprises a thirdlayout pattern; the third layout pattern has an edge overlapping thecell boundary of the layout design; and a second corner of the firstlayout pattern on the edge of the first layout pattern and a corner ofthe third layout pattern on the edge of the third layout patternabutting each other.
 8. The method of claim 1, wherein the electricalcharacteristic tuning process comprises a threshold voltage tuningprocess or a gate structure trimming process.
 9. A method of forming alayout design for fabricating an integrated circuit (IC), the methodcomprising: identifying one or more areas in the layout design occupiedby one or more segments of a plurality of gate structure layout patternsof the layout design, the one or more areas corresponding to one or moreregions of the IC subject to an electrical characteristic tuning processfor fabricating the IC, the plurality of gate structure layout patternsextending along a first direction and having a predetermined pitchmeasurable along a second direction, and the predetermined pitch beingsmaller than a spatial resolution of a predetermined lithographictechnology; and generating a set of layout patterns overlapping theidentified one or more areas, the set of layout patterns correspondingto one or more openings to be formed in a mask layer prior to performingthe electrical characteristic tuning process, a first layout pattern anda second layout pattern of the set of layout patterns being separated bya first gap along the second direction, and a width of the first gapmeasurable along the second direction being less than twice thepredetermined pitch.
 10. The method of claim 9, wherein the width of thefirst gap equals the predetermined pitch.
 11. The method of claim 9,wherein a third layout pattern and the first layout pattern of the setof layout patterns being separated by a second gap along the seconddirection, and a width of the second gap measurable along the seconddirection being an integer multiple of the predetermined pitch.
 12. Themethod of claim 9, wherein the first layout pattern has a widthmeasurable along the second direction, and the width of the layoutpattern is an integer multiple of the predetermined pitch.
 13. Themethod of claim 9, wherein the electrical characteristic tuning processis usable for leakage reduction of a dummy transistor of the IC or poweradjustment of a functional transistor of the IC.
 14. The method of claim9, wherein the set of layout patterns comprises a third layout pattern;the first layout pattern has an edge overlapping a cell boundary of thelayout design; and the third layout pattern has an edge overlapping thecell boundary of the layout design.
 15. The method of claim 14, whereinthe edge of the first layout pattern and the edge of the third layoutpattern abutting each other.
 16. The method of claim 14, wherein a firstcorner of the first layout pattern on the edge of the first layoutpattern and a corner of the third layout pattern on the edge of thethird layout pattern abutting each other.
 17. The method of claim 16,wherein the set of layout patterns further comprises a fourth layoutpattern; the fourth layout pattern has an edge overlapping the cellboundary of the layout design; and a second corner of the first layoutpattern on the edge of the first layout pattern and a corner of thefourth layout pattern on the edge of the fourth layout pattern abuttingeach other.
 18. The method of claim 9, wherein the electricalcharacteristic tuning process comprises a threshold voltage tuningprocess or a gate structure trimming process.
 19. A layout design forfabricating an integrated circuit (IC), comprising: a first layoutlayer, comprising a plurality of gate structure layout patterns, theplurality of gate structure layout patterns extending along a firstdirection and having a predetermined pitch measurable along a seconddirection, and the predetermined pitch being smaller than a spatialresolution of a predetermined lithographic technology; and a secondlayout layer, comprising a set of mask layout patterns arranged based onone or more opening regions, the one or more opening regions overlappingone or more of the plurality of gate structure layout patternscorresponding to one or more gate structures subject to an electricalcharacteristic tuning process, a first mask layout pattern of the set ofmask layout patterns having a width measurable along the seconddirection, and the width of the first mask layout pattern being equal tothe predetermined pitch.
 20. The layout design of claim 19, wherein asecond mask layout pattern of the set of mask layout patterns has awidth measurable along the second direction, and the width of the secondlayout pattern being an integer multiple of the predetermined pitch.